SCORU/Node: use local information to compute reorganizations
Context
Fixes #4903 (closed).
Use information stored locally by the rollup node about the old chain to compute reorganizations. This prevents the rollup node from stopping even if some blocks become unavailable on the Layer 1 Tezos node.
Manually testing the MR
dune exec tezt/tests/main.exe -- -f sc_rollup.ml -t 'Alpha: arith - rollup node - correct handling of commitments (handles_chain_reorgs_missing_blocks)'